Stacked bar chart
Stacked bars show composition within a category — revenue per region as fractions of the quarterly total. Normalized mode divides each segment by its band's total, producing 100%-stacked bars where every band reaches the plot top.
The demo plots the Apollo program's annual outlay by NASA centre, 1962–1972 ($B in 1973 dollars). Same dataset the grouped-bar chapter shows side-by-side, but stacked: total program spend per year reads off the top of each bar, and the Marshall (Saturn V) slice growing through 1966 before tapering tells the program-arc story in one chart.
Source: Apollo program — Costs — Wikipedia
Public surface
use wisp_chart::plot::Transform;
let plot = Plot::new(rows)
.mark(Mark::Bar { value_labels: false })
.encode(plot::x("quarter", ScaleKind::Band))
.encode(plot::y("revenue", ScaleKind::Linear))
.encode(plot::color("region"))
.transform(Transform::Stack { normalize: false });Two modes from one transform
Transform::Stack { normalize } | Behaviour |
|---|---|
false | Cumulative absolute values — Q1 stack hits Q1 total |
true | Each band rescaled to the y-domain top — every bar reaches 100% |
The renderer walks rows in DataFrame order, accumulating a
per-band cumulative offset. The first row for a band sits at the
baseline; subsequent rows stack on top. The series colour comes
from the Color encoding's palette lookup.
Pairing with Legend
Use Plot::legend
to auto-emit a legend that maps colours to series — same shape as
grouped bars, and the legend's swatches use the same palette
positions as the stacked segments.
Stack + XOffset = grouped-stacked
Combining Transform::Stack with Encoding::XOffset is allowed:
each outer X band is sub-banded by XOffset, and within each
sub-band the rows stack by Color. Useful for "stacked by
component within grouped by quarter" layouts.